ANTI-AIRCRAFT GUN WITH CAMERA

Abstract: A device for aiming at a mobile target (4) and directing an anti-aircraft gun (1) is described. The direction of the barrel is adjustable in azimuth and elevation manually with handle or by means of servo-controlled motors (2). A ranging unit is mounted in a support, manually operated, directly or via servo-motors, pivotable in azimuth and elevation. It comprises a sight (3), preferably field-glasses, for optical aiming at the target along an aiming line (5), and a range finder (6) pivotable in azimuth. The device shows means (7, 11) for direct or indirect measuring of the angular rate of the aiming line in azimuth or elevation. Said means are arranged to emit signals, corresponding to their respective measured values, to a calculating unit (8), which is arranged guided by said received signals and information given about correction values, such as the ballistic data from the projectile fired from the anti-aircraft gun, prevailing wind vector, to calculate the required lead and offset angles of the direction of the barrel, and to emit corresponding signals for setting the direction of the barrel, preferably to said servo-controlled motors, so that a fired projectile shall hit the target. The device is primarily characterized in that a camera means (9) is arranged parallelly with said aiming line (5) connected to a correlation means (10) with which the displacement in azimuth and elevation of the camera picture of the target (4) relative to the aiming line (5) is determined in the form of a correction signal, with which said measured angular rate of the aiming line in azimuth and elevation is corrected.

Description: ANTI-AIRCRAFT GUN WITH CAMERA The present invention relates to a device for aiming at a mobile target and directing an anti-aircraft gun or the like towards same, the firing direction of the barrel of the anti-aircraft gun being adjustable in azimuth and elevation, preferably by means of servo-controlled motors, with a ranging unit, comprising a sight, preferably field-glasses, for optical aiming at the target along an aiming line, and a means for ranging to the target, preferably of laser type, the ranging unit being mounted in a support, manually pivotable in azimuth and elevation, while the device shows means for direct or indirect measuring of the angular rate of the aiming line in azimuth or elevation, said means being arranged to emit signals, corresponding to their respective measured values, to a calculating unit, which is so arranged that with the aid of said received signals and information given about correction values, such as the ballistic data of the projectile fired frc the anti-aircraft gun, the prevailing wind vector, it calculates the required lead and offset angles of the direction of the barrel and emits corresponding signals for setting the direction of the barrel, preferably to said servo-controlled motors, so that a fired projectile shall hit the target. Such sights are known for example from Swedish patent specification SE 8503860-2. Therein, an anti-aircraft sight for aiming at a mobile target is described, comprising among other things a manually operated ranging unit, an aiming unit fixed to the gun and a calculating unit. A first operator strives to follow the target with the ranging unit, whereby measurement data with regard to the distance to the target and the movement of the target in azimuth and elevation via the calculating unit affects the relative setting between the aiming unit, which is kept directed at the target by a second operator, and the barrel of the anti-aircraft gun, so that the setting will be such, with regard to the lead and offset angles, that a fired projectile shall hit the target. In Swedish patent specification SE 9101148-6 an anti-aircraft sight is described, in which the ranging unit is pivotally mounted in a support, attached in the barrel, in which arrangement only one operator is needed for the aiming operation at the anti-aircraft gun. The ranging unit is here manouevered through direct, manual action, but devices of the kind mentioned in the introduction are also known at which the ranging unit is acted upon manually, via a stick, which via servo-motors sets the ranging unit in azimuth and elevation. See for example US 4,266,463. The device according to the invention comprises such embodiments too. In both types of sights for anti-aircraft guns there is the problem during aiming, that the operator by the ranging unit has difficulties in directing the aiming line at the identical point on the target, which takes up a certain space angle in azimuth as well as in elevation. In practice one must take into account that the aiming line swings over the target at a frequency of about one Hz and an amplitude corresponding to about one mradian. This fact gives a contribution of error in the measuring of the angular rates in azimuth and elevation, i.e. the target track. Thereby, one is forced to effect the ranging of the target during rather a long time, in the order 2-4 seconds so that sights of this kind shall function in the way intended. It would, however, be desirable that the ranging could be effected in a shorter time. Η-ie object of the present invention is therefore to provide a sight, i.e. a device, of the kind mentioned in the introduction, that admits a quick, safe ranging of the target track. According to the invention, such a device is primarily characterized in that a camera means is arranged directed parallelly with said aiming line, the camera means being connected to a correlation means with which the displacement in azimuth and elevation of the camera picture of the target relative to the aiming line is determined in the form of a correction signal, by which said measured angular rate in azimuth and elevation is corrected. With a picture angle on the camera used in the order 5°-10°, an accuracy is obtained of the ranging to the target of about 0.1 to 0.3 mradians, i.e. a factor of about 5-10 times better than whan can be obtained with sights of the kind mentioned in the introduction. This means that already after two rangings the barrel of the anti-aircraft gun can be set so that a projectile can be fired after a short time with a correct aiming in azimuth and elevation for it to hit the target. The invention is described in more detail in the following with reference to the accompanying figures, of which Figure 1 shows schematically in the form of a block diagram an embodiment of the device, whereas Figure 2 shows schematically a correlation means according to the invention * In the Figure the barrel of an anti-aircraft gun is designated by 1. Its direction is adjustable in azimuth and elevation by means of servo- controlled motors 2. In a support, a ranging unit is arranged, manually operated pivotable in azimuth and elevation. It comprises an optic sight 3 for optical aiming at a target 4 along an aiming line. Furthermore it comprises a range finder of laser type 6 for ranging to the target. Angular-velocity-sensing gyros, so-called rate gyros 11 are arranged to measure the angular rate of the barrel in azimuth and elevation. Means 7 measures the angle in azimuth and elevation between the aiming line of the ranging unit and the direction of the barrel. This embodiment of the device for aiming according to the invention thus works with indirect measuring of the angular rates of the aiming line. An embodiment is also possible in which the rate gyros are attached on the ranging unit, so that a direct measurment of the angular rates of the aiming line is obtained. A calculating unit 8 receives signals, corresponding to measured values frcm the range finder, the rate gyros and the means for angular measurement and receives in addition the signals, corresponding to the correction values, such as ballistic data about the fired pro¬ jectile, prevailing wind vector etc. The calculating unit calculates, guided by provided data, the required lead and offset angles of the barrel 1 and emits corresponding signals to said servo-controlled motors 2 for a fired projectile to hit the target 4. In order to iπprove accuracy in this calculation and compensate for the difficulty for the operator who manually controls the ranging unit to aim at the identical point on the target, a camera 9 is arranged for use in the day and/or night, for example of CCD type arranged parallelly with said sight 3 and range finder 6. The camera stands in connection with a correlation means 10 of known type. This works like this: a displacement in azimuth and ele¬ vation of the camera picture of the target 4 relative to the aiming line 5 gives rise to a correction signal, which is given to the calculating unit for correcting the data regarding the angular range of the aiming line in azimuth and elevation that the calculating unit received with he aid of the rate gyros and the means for angular measuring. In Figure 2 an example is shown of correlation means 10 in connection with a camera 9 and a calculating unit 8. From the signal received frcm the camera 9 the target is filtered out in a similar manner as in a conventional simple video target tracker in a picture filtration unit 12. This occurs through suitable filtration, thresholding, and a choice of target close to the center of the picture. The position in the picture of the target is then calculated in a position calculating unit 13, frcm which goes a signal partly to a memory unit 14 which stores a first picture, and partly to a difference unit 15, in which a subsequent, i.e. second picture is compared with said first picture (correlation), differences in side and height becoming the starting values for the desired correction. The correction signal then goes onwards to a correction filtering unit 16, which can be formed in different ways. It can comprise a median filter for the elimination of erroneous signal values, followed by a Kalman filter adapted to the occurring, manually caused movement dynamics in the sight, with the task to eliminate noise. This latter filter works with higher sampel frequency than the video signal frcm the camera 9 in order to make possible that the correction can be trans¬ mitted without beats to the calculating unit 8, which is not synchronized with the video signal. It should be mentioned that another type of anti-aircraft gun has been suggested by the company Sagem in US 4,922,801. Here is suggested a sight mounted on the barrel of an anti-aircraft gun. The sight comprises a reticle which can be adjusted in its position relative to the direction of the barrel. A camera is attached to the barrel with its field of vision coaxial with the direction of the barrel. The movement of the target in the field of vision of the camera is measured as the angular movements of the barrel. The position which shall be given to the reticle is calculated frcm variations of the aiming direction and the movement of the target in the field of vision of the camera, and the position of the reticle is adjusted accordingly. The principle of Sagem's anti-aircraft sight is thus entirely different from the here described device for aiming. According to it, the sight is not mechanically locked to the barrel, which admits aiming at the target simultaneously with the barrel following the lead point. Furhermore, with the device, better accuracy is obtained, because sight and camera can be used with greater angular resolution when the camera is arranged parallelly with the aiming line and not parallelly with the barrel. Furthermore with the device according to the invention, shorter reaction time is obtained when the gun is guided autαnatically towards the lead point when sufficient data have been measured. According to Sagem the barrel is controlled in that after calculation of the target track, the operator again puts the target over the reticle that the system has calculated. The device according to the invention is also simple in its construction, because only one correlation means is needed which measures the position of the target in pairs of subsequent pictures. As described above, the obtained difference gives rise to a correction signal, which admits safe aiming also if the operator is not capable of aiming at the same point of the target during the ranging phase.

Claims: Claims 1. A device for aiming at a mobile target (4) and directing an anti¬ aircraft gun (1) or the like at same, the direction of the barrel of the anti-aircraft gun being settable in azimuth and elevation, preferably by means of servo-controlled motors (2) , with a ranging unit, coπprising a sight (3), preferably field-glasses, for optical aiming at the target along an aiming line (5) and a means (6) for ranging to the target, preferably of laser-type, the ranging unit being mounted in a support manually operated pivotable in azimuth and elevation, while the device shows means (7, 11) for direct or indirect measuring of the angular rate of the aiming line in azimuth or elevation, said means being arranged to emit signals corresponding to their respective measured values, to a calculating unit (8) which is arranged guided by said received signals and information given about correction values, such as the ballistic data of the projectile fired from the anti-aircraft gun, prevailing wind vector, to calculate the required lead and offset angles of the direction of the barrel, and to emit corresponding signals for setting the direction of the barrel, preferably to said servo-controlled motors, so that a fired projectile shall hit the target, c h a r a c t e r i z e d in that a camera means (9) is arranged directed parallelly with said aiming line (5), the camera means being connected to a correlation means (10) with which the displacement in azimuth and elevation of the camera picture of the target relative to the aiming line is determined in the form of a correction signal, with which said measured angular rate of the aiming line in azimuth and elevation is corrected. 2. A device according to claim 1, c h a r a c t e r i z e d in that a correction filtering unit (16) ccmprising a median filter for eliminating erroneous signal values is arranged to filter the correction signal frcm the correlation means (10) . 3. A device according to Claim 1 or 2, c h a r a c t e r i z e d in that a correction filtering unit (16) comprising a Kalman filter for eliminating noise caused by the manual operation, that is the movement, of the aiming line (5) is arranged to filter the correction signal frcm the correlation means (10) .

Inventors: NILSSON BERTIL, NILSSON, BERTIL
Applicants: NILSSON BERTIL, SAAB INSTR AB, NILSSON, BERTIL, SAAB INSTRUMENTS AKTIEBOLAG
Application year: 1994
Main classification: F41G3
IPC codes: F41G3, F41G5